1. Technical Field
The disclosure generally relates to a display panel and a fabricating method thereof, in particular, to a transflective LCD panel and a fabricating method thereof.
2. Description of Related Art
Along with the popularization of LCDs (Liquid Crystal Displays), many portable electronic products have higher requirements for the display function of the LCDs. For example, the portable electronic products are required not only to provide a fine frame display effect indoors, but also to maintain an appropriate display quality in high light environments. Therefore, the LCD technology is developed in the trend of maintaining a vivid display quality of an LCD in high light environments. In view of the above-mentioned, a transflective LCD is preferred as it can provide vivid display effects both indoors and in a bright outdoor environment.
In detail, the conventional transflective LCD panel generally adopts a dual cell gap design, in which the transmissive region and the reflective region both have a fine display quality. However, the fabrication of the transflective LCD panel with the dual cell gap design is complex, and each pixel unit has poor transmittance at the junctions areas between the transmissive regions and reflective regions. Therefore, the transflective LCD panel with a single cell gap design is desired.
FIG. 1A is a cross-sectional view of a conventional transflective LCD panel with the single cell gap design, and FIG. 1B is a schematic view of a pixel unit in FIG. 1A. Referring to FIGS. 1A and 1B together, the conventional transflective LCD panel 100 includes a thin-film transistor (TFT) array substrate 1100, a color filter substrate 1300, and a liquid crystal layer 1200 disposed therebetween. Further, the color filter substrate 1300 includes a substrate 1310, a color filter 1320, a common electrode layer 1330, and an alignment film 1340. The color filter 1320 is disposed on the substrate 1310, the common electrode layer 1330 is disposed on the color filter 1320, and the alignment film 1340 is disposed on the common electrode layer 1330.
The TFT array substrate 1100 includes a substrate 1110, a plurality of scan lines 1120, a plurality of data lines 1130, a plurality of pixel units, and an alignment film 1150. The scan lines 1120, data lines 1130, and pixel units are disposed on the substrate 1110. The alignment film 1150 is disposed on the substrate 1110, and covers the scan lines 1120, data lines 1130, and pixel units. In detail, each pixel unit includes a TFT 1142, a transparent pixel electrode 1144a, a reflective pixel electrode 1144b, and a dielectric layer 1146. The TFT 1142 is electrically connected to the corresponding scan line 1120 and data line 1130. The reflective pixel electrode 1144b and the transparent pixel electrode 1144a are disposed on the dielectric layer 1146. Moreover, the reflective pixel electrode 1144b is connected to the transparent pixel electrode 1144a, and the transparent pixel electrode 1144a is electrically connected to the TFT 1142. In addition, the alignment film 1150 covers the reflective pixel electrode 1144b and the transparent pixel electrode 1144a. 
Light rays 10a emitted by a backlight source (not shown) sequentially pass through the substrate 1110, the transparent pixel electrode 1144a, the liquid crystal layer 1200, and the common electrode 1330, and then emerge from the substrate 1310. Furthermore, light rays 10b from a front light source or an external environment may also sequentially pass through the substrate 1310, the common electrode 1330, and the liquid crystal layer 1200 and reach the reflective pixel electrode 1144b. Afterwards, the light rays 10b reflected by the reflective pixel electrode 1144b further sequentially pass through the liquid crystal layer 1200 and the common electrode 1330, and emerge from the substrate 1310.
FIG. 2 shows a driving voltage to transmittance ratio (V-T) curve of a conventional transflective LCD panel with the single cell gap design. Referring to FIGS. 1A and 2 together, since each pixel unit has a transparent pixel electrode 1144a and a reflective pixel electrode 1144b, the conventional transflective LCD panel 100 has a transmissive region V-T curve T and a reflective region V-T curve R. The transmittance ratio is a ratio between a light transmittance value and the maximum light transmittance value of the reflective or the transmissive region. Generally, the light transmittance of the reflective or the transmissive region represents a display brightness of the reflective or the transmissive region. However, at the same driving voltage, the transmittance ratio of the transmissive region V-T curve T is different from that of the reflective region V-T curve R. Moreover, a driving voltage V2 required by the transmissive region for reaching its maximum light transmittance is different from a driving voltage V1 required by the reflective region for reaching its maximum light transmittance. Further, since an optical path of the liquid crystal layer in the transmissive region is approximately a half of that of the liquid crystal layer in the reflective region, when the light transmittance ratio of the transmissive region grows and reaches the maximum value along with the increase of the driving voltage, the transmittance ratio of the reflective region has already passed the maximum value and began to gradually decrease with the increase of the driving voltage.
In order to solve the above problems, a technique of adjusting the status of capacitance of the liquid crystal molecules arranged in series in the reflective region to reduce the voltage difference originally generated between the reflective pixel electrode and the common electrode layer by a driving voltage is provided. More particularly, the driving voltage required by the reflective region for reaching the maximum transmittance is made larger than the driving voltage V1 in FIG. 2. Therefore, the status of capacitance of the liquid crystal molecules arranged in series in the reflective region may be appropriately adjusted to make the driving voltage required by the reflective region for reaching its maximum transmittance approximate to the driving voltage required by the transmissive region for reaching its maximum transmittance, as shown in FIG. 3.
However, when the driving voltage required by the reflective region for reaching its maximum transmittance is increased, a threshold driving voltage (the voltage turning on the transmittance) required by the reflective region is also increased accordingly, and the addition of the threshold voltage differs from that of the driving voltage for reaching the maximum transmittance. That is, the above conventional technique cannot make both the threshold voltage of the reflective region and the driving voltage required by the reflective region for reaching its maximum transmittance simultaneously approximate to the threshold voltage of the transmissive region and the driving voltage required by the transmissive region for reaching its maximum transmittance (as shown in FIG. 3). As such, the transflective LCD panel cannot have the optimal optical performances in both of the transmissive state and the reflective state simultaneously. Accordingly, there is a need for a transflective LCD panel and fabricating method that can solve the problem of the inconsistency of driving characteristics of the reflective region and the transmissive region in both a bright state and a dark state.